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End of Chapter Answers

Reviewing the Concepts Answers

  1. Describe the structure of DNA. DNA is a double helix of covalently bonded nucleotide strands. The two strands run anti-parallel to each other and are hydrogen bonded to each other.
  2. Explain why complementary base pairing is crucial to exact replication of DNA. During replication the two DNA strands unwind and new nucleotides are added to make two new strands. Complimentary base pairing is needed to make sure that each strand is exactly alike.
  3. Why is DNA replication described as semiconservative? One strand is new and one strand is from the original DNA.
  4. Explain the roles of transcription and translation in converting the DNA message to a protein. Transcription of DNA is when a mRNA template is produced. The mRNA template codes for the production of amino acid chains during translation.
  5. In what ways does RNA differ from DNA? RNA is single stranded, the nucleotide sugar is ribose, and uracil replaces thymine.
  6. What roles do mRNA, tRNA, and rRNA play in the synthesis of protein? mRNA carries the transcribed message to the ribosomes. tRNA carries the amino acids to the ribosomes for assembly. rRNA assembles the amino acids.
  7. Define codon. What role do codons play in protein synthesis? A codon is a three nucleotide sequence that codes for a specific amino acid. Codons are read from the mRNA to produce amino acid chains.
  8. What is the role of an anticodon? The anticodon is carried by tRNA. The anticodon pairs with the codon on the mRNA
  9. Describe the events that occur during the initiation of protein synthesis, the elongation of the protein chain, and the termination of synthesis.
    1. Initiation – small ribosomal subunit joins with the mRNA start codon. Complimentary tRNA joins with the start codon and the large subunit joins to form a functional ribosome. tRNA continues to pair with the codons to produce a chain.
    2. Elongation – the chain continues to grow
    3. Termination – occurs when a stop codon is encountered. The ribosomes separate and the process is terminated.
  10. What is a point mutation?  A point mutation is the substitution of one nucleotide pair for another nucleotide pair in the DNA.
  11. How is gene activity regulated?  Gene activity is regulated by chromosomal coiling and uncoiling, regulatory genes, and chemical signals such as hormones.
  12. Define genetic engineering. Explain the roles of restriction enzymes and vectors in genetic engineering. Genetic engineering is the manipulation of genetic material for human purposes. Restriction enzymes cut out pieces of DNA according to the nucleotide sequence they recognize. Vectors are biological carriers of recombinant DNA to the new host cell.
  13. Describe some of the ways in which genetic engineering has been used in farming and medicine. Genetically engineered crops are being used more end more. They are disease resistant, drought resistant, and pest resistant. Vaccines, therapeutic proteins and some antibodies are genetically engineered
  14. What is gene therapy? therapy attempts to deliver functional DNA to cells that are not functioning correctly. The usual method is to use a virus to deliver the DNA.
  15. a
  16. c
  17. b
  18. a
  19. tRNA
  20. uracil
  21. restriction enzymes

Hints for Applying the Concepts Questions

  1. Hint: What is the start codon? What is the stop codon? What amino acids do the other codons code for?
  2. Hint: Translate each of the mRNA strands. Remember that more than one codon can code for the same amino acid.
  3. Hint: Are any bands present in a father, but absent in both the mother and the child?

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